1. Field of the Invention
The invention relates to an image forming apparatus having a pre-paper-feed function to previously feed a paper to a predetermined position on a conveying path before a print request.
2. Related Background Art
The inventor of the present application has already proposed an image forming apparatus having a pre-paper-feed function with a construction as shown in FIG. 6. The function of each section will now be described hereinbelow.
Reference numeral 100 denotes a photo sensitive drum as an electrostatic latent image holding member; 101 a charging roller to uniformly charge the drum 100; 102 a developing device to develop an electrostatic latent image formed on the drum 100 by a light beam 104; 103 a copy transfer roller to copy transfer the developed toner image onto a paper; 105 a semiconductor laser to generate the light beam 104; 106 a scanner to scan the light beam 104 onto the drum 100; 107 an optical lens system to adjust the light beam so as to form a light spot on the drum 100. As shown in FIG. 7 a controller 202 is used for transmitting a command to a printer control unit 203, and for reading out internal data as a status from the printer control unit 203. The controller 202 also sends a print start request or a pre-paper-feed request to the printer control unit 203 and further transmits and receives a sync signal to synchronize the output timing of the image data and the conveyance timing of the paper in the printer. The controller 202 is provided in either the printer or the host computer. Reference numeral 203 denotes the printer control unit 1 which transmits and receives control signals to/from the controller 202 and also controls the timings to drive/stop each mechanism section in FIG. 6 and reads out input information from each sensor. Reference numeral 204 denotes an operation panel, which is used for the user to input various kinds of setting modes of the printer (for instance, the setting of a margin in an image region and the like). The operation panel 204 is generally used in an off-line state (state in which the communication line 202 with the host computer is disconnected).
Reference numeral 205 denotes a feed system drive unit to drive/stop a drive/stop motor 210 of various rollers 211 on the basis of an instruction from the printer control unit 203. Reference numeral 206 denotes drum surface; 108 a paper cassette in which papers to be printed are enclosed; 109 a paper feed roller to take out the papers from the cassette 108 one by one and convey to the conveying path; 110 a resist paper presence/absence sensor to detect the presence or absence of the paper on the conveying path; 111 resist rollers for correcting the oblique movement by abutting the front edge of the paper to the resist rollers and for synchronizing the timing to write image data onto the photo sensitive drum and the timing to convey the paper; 112 a fixing roller to fuse and fix the toner image, which has been copy transferred to the paper, onto the paper; 113 a discharge paper presence/absence sensor to confirm that the paper is discharged from the fixing roller; and 114 paper discharge rollers to discharge the paper.
FIG. 7 shows a block diagram of a control system to control an electrophotographic printer having a mechanism section as mentioned above.
Reference numeral 200 denotes a host computer to transmit image code data formed by the operation of the user or the like on the outside of a printer to the controller 202 as parallel or serial data through a communication line 201. Reference numeral 202 denotes the controller for developing the image code data sent from the host computer 200 and converting it into image data using a high voltage system drive unit to drive/stop a charging unit 212, a developing unit 213, and a copy transfer unit 214 on the basis of an instruction from the printer control unit 203; 207 indicates an optical system drive unit to drive/stop a laser 215 and a scanner 216 on the basis of an instruction from the printer control unit 203; 208 a fixing heater control unit to drive/stop a fixing heater 217 on the basis of an instruction from the printer control unit 203; and 209 a sensor input unit for reading information from a resist sensor 218 and a paper discharge sensor 219 and providing the information to the printer control unit 203.
FIG. 8 is a flowchart showing a sequence for a pre-paper-feed from the stand-by of the printer control unit to the printing of one page.
The printer is first held in a waiting state for a print signal from the controller 202. When no print signal is received, the presence or absence of a pre-paper-feed request from the controller is checked. When the pre-paper-feed request is received, the motor is driven and, thereafter, the paper feed operation is started. A check is subsequently made to see if the paper has reached the position of the resist sensor or not. After the sensor has detected the front edge of the paper, the apparatus waits for T.sub.0 seconds (time which is required until the front edge of the paper of a predetermined amount abuts on the resist rollers) and the paper feed operation is stopped. The motor is also stopped at this time point and the apparatus enters the print signal waiting state. When the print signal is received, the motor is again driven and the scanner and each high voltage system is raised. When the rotational speed of the scanner motor reaches a predetermined value, the paper has already previously been fed, so that the presence or absence of the paper of at the resist sensor is checked. Since the pre-paper feed has already been executed here, when no paper exists at the position of the resist sensor at this time point, an abnormality process (jam process or the like) is performed. When the paper exists at the position of the sensor, a vertical sync request signal is generated to the controller 202. When the controller 202 receives the vertical sync signal after that, it permits the image writing operation onto the photo sensitive drum and drives the resist rollers. When the paper discharge sensor detects the trailing edge of the paper, the apparatus waits for T.sub.i seconds (time which is required until the paper is completely discharged from the apparatus). Then, the high voltage is dropped, the scanner motor is stopped, the motor of the roller drive system is stopped, and the printing process is stopped.
The above description relates to the case of the single printing mode. FIG. 9 shows a timing chart for the printing operation by the pre-paper-feed request signal and the print signal in the case of a continuous printing mode. The pre-paper-feed request signal is generated as a pulse signal having a predetermined width. In the continuous printing mode, the controller can previously feed a necessary number of papers, which will be printed subsequently during the printing operation of a certain paper. However, the printer control unit 203 feeds the paper while keeping an interval of a predetermined amount for the preceding paper. Therefore, there is a case where it takes a short time until the paper is actually fed after the controller generates the pre-paper-feed request signal (such a time is shown by T.sub.d in the diagram). Hitherto, there are executed processes such that when the printer control unit once receives the pre-paper-feed request signal, the paper feed operation is certainly executed at a predetermined timing.
In the conventional apparatus mentioned above, however, there is a processing system such that in response to the pre-paper-feed request, which has once been generated from the controller, the pre-paper-feed is certainly executed for the printer at a predetermined timing.
For instance, therefore, when the user operates the operation panel connected to the controller, the user sets the apparatus into the off-line state and executes an operation such as a mode change or the like. However, when the off-line setting operation is performed after the controller generated the pre-paper-feed request, the controller cannot make such a request invalid. Accordingly, the apparatus waits until the printer feeds the paper. Thereafter, the controller generates a print signal and waits for the completion of the printing operation and must cope with the off-line operation by the user. Such an operation to make the pre-paper-feed invalid is considered to be executed not only in the case of the off-line operation but also the cancelling operation of the image data, which is performed from the host computer side to the controller or the like. That is, according to the conventional technique, when the pre-paper-feed request, which has once been generated from the controller, needs to be made invalid due to some cause, such a request cannot be made invalid. Thus, a problem occurs from a viewpoint of the operating efficiency of the user as mentioned above when such a process to make the pre-paper-feed request invalid is impossible.